Woven fabrics that are 100% synthetic (e.g., polyesters, polypropylene, nylon, acrylic and elastane fibers), with a tight surface, are a good receptive fabric choice for dye sublimation heat transfer applications. However, 100% synthetic fabrics make poor articles of apparel, and poor non-apparel items (e.g., napkins, tablecloths or aprons), because these fabrics are hydrophobic and repel or are resistant to moisture, and tend to be harsh to the touch.
Some newer 100% polyester fabrics, with hydrophilic wicking ability, have been produced with the intent of addressing these concerns. Several methods are used in order to make synthetic fabrics more amenable to wicking moisture (i.e., make them more hydrophilic).
One method to make synthetic fibers more hydrophilic is to treat them with a wicking agent. These fibers can then be made into yarn that is then constructed into fabric. The resulting fabric is then hydrophilic.
Alternatively, hydrophobic fibers can be made into yarn that is then treated with a wicking agent. When constructed into fabric, this yarn makes the fabric hydrophilic.
Finally, a hydrophobic fabric can be treated with a wicking agent to make it more hydrophilic.
Regardless of the method used to make synthetic fabrics more hydrophilic, many wicking agents or treatments usually wash out after a few washes, and others have been permanently damaged or neutralized after exposure to severe temperature, pressure and dwell time (such as when undergoing a dye sublimation heat-transfer application—exposure to about 400 degrees Fahrenheit and to about 50 pounds of pressure per square inch, more or less, for approximately thirty seconds), and still others may not perform as well.
Until recently, the only fabric available for dye sublimation heat transfer applications that was also suitable for apparel use, was a “plated” fabric. This fabric is made on a double-knit knitting machine. This knitting machine is set up to produce a knit fabric having two distinct sides with different fabric compositions. One example is where the surface or face side is 100% polyester, and the reverse or backside is 100% cotton. The actual blend of the fabric would be 50% polyester, 50% cotton. Although this fabric is print receptive, and the reverse or backside of the fabric (cotton side) is hydrophilic, or receptive of moisture, the fabric demonstrates a slightly lower resolution for a dye sublimation heat transfer print, when compared to another fabric that is 100% synthetic and has the identical heat transfer applied. This is because of slight “grin through”, or the phenomenon where some of the cotton fibers from the reverse, or backside of the fabric, come through to the surface of the fabric.
Cotton fibers do not readily accept the sublimable dyes and the sublimable dyes are not fully colorfast on cotton. In addition, because the polyester side of the fabric remains hydrophobic, it could be uncomfortable when made into apparel. The hydrophobic surface of the polyester can act like a shield or barrier to the cotton side of the fabric, and inhibit the transmission of moisture through to the surface. Also, after going through the process of a dye-sublimation transfer application, the surface of the fabric plates becomes shiny and very slick (or slimy) to the touch. In addition, the plated fabrics tend to shrink more than polyester.
The formula for dye sublimation heat transfer application varies, and depends on the transfer manufacturers' directions. There are many types of dyes and paper substrates that can be used in the manufacture of the heat transfers, in addition to many different ways to make the transfers. Time of application can vary from a low of about 15 seconds to a high of about 35 seconds. Pressure from the application can also vary from a low of about 20 psi, to a high of about 50 psi. Temperatures can also vary from about 340 F to about 400 F, or more.
There is a need in the market place for truly “no-care”, synthetic-rich fabrics that are highly adaptive and print receptive, having the hydrophilic characteristics necessary to withstand the severe conditions of the dye-sublimation heat-transfer process, in addition to having other characteristics that will allow the fabrics to withstand the many washings that will follow, both domestic and commercial/industrial. For apparel, additional desirable characteristics include: functional, comfortable, soft cotton-like feel, affordable, stylish, zero to low shrinkage, ease of cleaning, stain and soil resistant, chlorine bleach resistant, wrinkle resistant, colorfastness, long lasting, durable, and UV protection. Many of the same characteristics that are desirable for apparel are desirable for non-apparel items.
Americans are more concerned about skin cancer than ever before. UV rays damage the skin in many ways, causing premature wrinkles, sunburn, cataracts and skin cancer. The Skin Cancer Foundation (www.skincancerfoundation.org), estimates that nearly 1,000,000 Americans will be diagnosed with skin cancer this year. In addition, one American per hour dies from skin cancer, mostly melanoma, and that 1 in 5 Americans will be diagnosed with skin cancer in their life times. California has the “Billy Law” requiring students in school to wear hats during outside activities. Many states now cover workmen's compensation claims from employees who work outside and develop skin cancer.
Wearing apparel with UV protection helps decrease the damage done by these rays. In warmer climates, it is important to have lighter weight clothing that is both comfortable to wear and has adequate UV protection. Although cotton is highly breathable and comfortable to wear, it proves to be an inadequate material for UV protection. Alternatively, polyester is an excellent material for UV protection, but in order to be comfortable, the fabric would also need to have wicking capabilities necessary for breathablity.
The FTC recently set standards to label apparel for UV protection, requiring that a UPF rating be determined. This standard is nearly identical to the SPF ratings given to sunscreen and cosmetics. UPF stands for “Ultra-violet Protection Factor”. A number is associated with the protective factor of the fabric. There are laboratory tests to determine the UPF rating of a fabric. One test is UV Protection Factor, AATCC 183-2000A. This FTC standard requires that 2 types of invisible UV rays be tested for penetration through the fabric. Both UVA and VB rays are measured. A rating of UPF15+ is the minimum rating of fabric that is allowed for labeling purposes. A rating of UPF 15+, means that less than of 1/15 of all UV rays penetrate the fabric and reach the surface of the skin, and represents a blockage of a minimum of 93.3% of all UV rays. A rating of UPF 50+ is the highest rating possible for labeling purposes of apparel, and means that less than 1/50 of all UV rays penetrate the fabric and reach the surface of the skin, and represents a minimum blockage of a minimum of 98% of all UV rays. There are three levels of protection (see table below).
UPF RATINGCATEGORY of PROTECTIONUV % BLOCKED  40-50+Excellent UV protection97.5%-98.0%25-35Very Good UV protection96.0%-97.4%15-20Good UV protection93.3%-95.8%
Most light weight cotton t-shirts and polo shirts only have a UPF rating of UPF 6 or 7. Certainly well under the minimum standards set by the FTC for UV protective clothing. At the present time, apparel that has a UPF40+ to UPF50+ rating is relatively expensive to manufacture. More often than not, these garments are of heavier weight and although they provide exceptional UV protection, are not really practical for warm, hot or tropical weather. There is a need in the market for lightweight %-shirts and polo shirts that have “Excellent” UPF ratings of UPF40+ to UPF50+, rated both dry and wet, with a high degree of wicking, and that are more economical to manufacture. These garments would also be perfect for babies and children, where sun block lotions must be constantly addressed throughout the day.
Iron-on heat transfers, and specifically, dye-sublimation heat-transfers, have been around for many decades. In the iron-on process, sublimable dyes are printed onto a substrate, such as paper. There are many ways to print these transfers, such as: rotary screen, flat screen, roller print or digital. This printed substrate (the dye sublimation heat transfer) is then placed onto a host fabric where it undergoes a process whereby specific heat and specific pressure are applied to the transfer and fabric, or article of apparel or non-apparel, for a specific period of time. The substrate is then removed and the image has been “transferred” into the host fabric. The dyes “explode” under heat and pressure, turning into a gas, and this gas dyes the synthetic fibers in the host fabric, or article of apparel or non-apparel.
A true “no care” article of apparel, or non-apparel item, having undergone a dye sublimation heat transfer process, should have the following beneficial or necessary characteristics: little to zero shrinkage, no twisting and/or torque after repeated washings, doesn't fade and is colorfast, stain and soil resistant, washable at home, pill resistant, wrinkle resistant, soft, chlorine bleach resistant, cotton-like feel, comfortable, resistance to bacteria, odor, mildew and fungus, wicking capability, and UV protection.